Technical Field
The invention relates to a magnetic drive pump, and more particularly to, a magnetic drive pump including a stationary shaft, and a metal pump casing with an anti-corrosion casing liner, in order to make the magnetic drive pump operate reliably at 200 degrees Celsius (° C.), and meet a high performance requirement for the magnetic drive pump when transferring fluid. Moreover, a one-piece casing with a stationary shaft supporting structure and a flow channel structure thereof, are improved for enhancing the supporting stiffness of the stationary shaft to reduce the temperature impact on a fluoropolymer component structure and for enhancing the performance, the reliability and life cycle of the magnetic drive pump.
Related Art
A sealless magnetic drive pump known to the skilled in the art is generally adopted for anti-corrosion or leakage prevention. In structure design, the magnetic drive pump includes either a stationary shaft or a rotary shaft. The supporting method for the stationary shaft includes a double-sided-supporting or a cantilever supporting structure, and the material of the stationary shaft support of the magnetic drive pump with stationary shaft is plastic material or a reinforced plastic material with metal; a front end and a rear end of the stationary shaft are supported by a triangle front support made of plastic and a sealed rear shaft seat of a containment shell, respectively. A fiber reinforce structure covers a bottom side of the containment shell. The stiffness of the plastic is decreased when the operating temperature rises as well as the stiffness of the triangle front support and that of the rear shaft seat are decreased accordingly, which makes the stationary shaft crooked and moved. The cantilever support at the rear end of the stationary shaft is supported by the metal-reinforce bottom side of the containment shell, the supporting stiffness comes from a radial force which is applied on the cantilever stationary shaft and spread to the containment shell, thereby reducing the deformation of the containment shell and enhancing the handling of the stationary shaft. However, the stiffness is limited by the temperature of the fiber reinforce plastic of the containment shell; the following prior arts further describes the problems and the potential problems about the stationary shaft of the magnetic drive pump.
Case 1:
U.S. Pat. No. 7,033,146: Sealed magnetic drive sealless pump, 2006. This patent describes a bearing design for dry-run condition. Figures in the invention indeed describes a conventional double-sided stationary shaft of the plastic magnetic drive pump and a triangle front support which is installed in the inner space of an inlet and extends axially through a hub aperture. A front shaft seat is positioned on the rear end of the triangle front support and on the inner side of the hub aperture for supporting one end of the stationary shaft. The patent tries to reduce the flow resistance of an inlet channel as much as possible by the triangle front support. The containment shell is a cup-shaped shell structure, and a rear shaft seat without any through hole is positioned on a bottom side of the containment shell for supporting the other end of the stationary shaft. The stiffness of the triangle front support and that of the containment shell are easily reduced because of increased temperature. As shown in the figure, in order to reduce the impact on the inlet channel by the triangle front support, the length of the triangle front support is deliberately extended so that front shaft seat passes through the hub aperture. But such a structure may reduce the strength of the triangle front support in the radial direction and should only be adopted in a device with lower power at low temperature.
Case 2:
U.S. Pat. No. 7,057,320: Mechanical drive system operating by magnetic force, 2006. This patent describes the structure and the design of an out rotor of a magnetic drive pump, and the figure of the invention distinctly shows a conventional double-sided-supported stationary shaft of a magnetic drive pump, and a triangle front support which is positioned in the inner space of an inlet and integrates with a pump casing in one piece by injection molding. The triangle front support extends axially towards the vicinity of an inlet of the impeller blade. A front thrust ring is installed on an end surface of a front shaft seat of the triangle front support, and a thrust bearing is installed on a hub plate and protrudes toward the inlet of the impeller. The containment shell is a cup-shaped shell structure, and a rear shaft seat without any through hole is positioned on a bottom side of the containment shell for supporting the other end of the stationary shaft. In order to reduce the flow resistance of the inlet channel from the front shaft seat of the triangle front support and the thrust ring, the diameter of the inlet of the impeller is increased to be greater than the inner diameter of the inlet of the pump so that the flow resistance may be reduced. But, the hub plate of the impeller and the front shaft seat are not in a smooth surface, and therefore it will interfere the flow at the leading edge of the impeller, and the lower flow resistance advantage is reduced.
Case 3:
CN Patent number CN2482597Y, Magnetic drive corrosion resistant fluoropolymer liner pump, 2002. The patent discloses a magnetic drive pump including a metal pump casing with a casing liner and describes the structure of the casing liner made of fluoropolymer and its use in corrosion resistance. The magnetic drive pump includes a shaft support integrated with the casing liner as one piece, wherein the casing liner is made of fluoropolymer. The containment shell made of fluoropolymer is a cup-shaped shell structure, and a rear shaft seat without any through hole is positioned on a bottom side of the containment shell for supporting the other end of the stationary shaft. However, the invention indicates that the supporting structure of the double-sided-supported stationary shaft which is made of fluoropolymer may be elastically deformed, and the vibration of the shaft may be eased when the pump operates. But the invention does not further describe whether the stiffness and the reliability of the structure may be applied up to a high temperature of 200° C.
Case 4:
U.S. Pat. No. 5,895,203: Centrifugal pump having separable multipartite impeller assembly, 1999. The patent discloses a magnetic drive pump including a metal pump casing with a plastic casing liner and a double-sided-supporting stationary shaft structure. A separable triangle front support is installed in the inner-diameter space of an inlet by an outer ring fitted in the inner ring surface of the inlet. A front shaft seat which is positioned at the center of the shaft support is used for offering the front-end support for a stationary shaft. The patent emphasizes the triangle front support including reinforcing material encapsulated within anti-corrosion material for enhancing the endurance of the front-end support of the stationary shaft when the triangle front support is subjected to force or vibration. Moreover, the patent further emphasizes that the diameter of the front end of the stationary shaft must be less than that of the rear end of the stationary shaft so that the outer diameter of the front shaft seat of the triangle front support may be reduced, and the surface of the nose is made into a smooth curve surface to meet with flowing requirement. When the front side of the stationary shaft is installed in the inlet of the pump, the resistance of the flow into the impeller may be reduced.
Case 5:
U.S. Pat. No. 6,280,156B1: Magnetically coupled rotary pump, 2001. The patent discloses an out-rotor type magnetic drive pump. The patent emphasizes that the vertical magnetic drive pump made of metal without plastic liner can drainage transferred fluid completely during maintenance. A stationary shaft is supported by a single-sided-supporting structure at the pump inlet which consists of a triangle front support and a cone-shaped front shaft seat. The triangle front support and the cone-shaped front shaft seat are formed onto or fixed on a metal pump casing. The cone-shaped front shaft seat is positioned in the inner space of the pump inlet so the inner diameter of the pump inlet must be increased to accommodate blockage of the cone-shaped front shaft seat and preserve essential space of the flow channel; a bearing of the impeller is installed in the inner space of an hub part axially extending towards the inlet and is used for mating with a sleeve at the rear end of the cone-shaped front shaft seat, and with a thrust ring. Thus, a curve surface of the cone-shaped front shaft seat which is gradually increased in an oblique direction may be connected to a curve surface of the axial hub part of the impeller smoothly, and furthermore the inlet of the impeller adopts a large-caliber design corresponding to the outer diameter of the axial hub part. Therefore, the case is feasible; but if the structure is to be adapted for highly anti-corrosion application, for example, hydrofluoric acid, then the metal pump casing must be made with a fluoropolymer liner, and the internal structure surface of the metal pump casing must be encapsulted with fluoropolymer, and the impeller must be made of fluoropolymer with metal reinforced. The minimum thickness of the liner and encapsulations must be at least 3 millimeters (mm), so the additional increase of the outer diameter of the cone-shaped front shaft seat will be twice of the 3 mm requirement. Similar increases apply to all other parts that are lined or encapsulated. If structural strength of the fluoropolymer is to be considered, the liner or encapsulation needs to be thicker. A metal reinforce plate is further installed in a hub plate of the impeller made of fluoropolymer, and comprises the axially extending axial hub part of the impeller for enhancing the structural strength and moment transmission, and furthermore a bearing which is installed in the inner space of the axial hub part is replaced by a ceramic bearing whose thickness is similar to that of the sleeve. Moreover, the inner diameter and outer diameter of the axial hub part are greatly increased because of the addition of the metal reinforce plate, the double-sided resin enclosure and the ceramic bearing. If only the cone-shaped front shaft seat is covered with the resin enclosure, the outer diameter of a cone curve surface must be increased accordingly, but is still much less than the outer diameter of the axial hub part with encapsulated liner, thus, the slope of a metal part of the cone-shaped front shaft seat must be adjusted by increasing its outer diameter to be smoothly connected to the curve surface of the axial hub part of the impeller. That is to say, the cylindrical inner surface in the inner space of the pump inlet must has greater expanding angle to meet with the curve surface of the cone-shaped front shaft seat and the outer diameter of the axial hub part. Therefore, the inlet of the impeller which has been adopted the large-caliber design must increase its size further, and fluid in the inlet of the pump must flow to the inlet of the impeller through a shorter axial distance and in the greater expanding angle. Regarding to such limitations, the metal pump having low flow resistance property may not be obtained and the design of the impeller is much more difficult; Another problem of the fluoropolymer impeller is that when the weight of the impeller is greatly reduced, the centroid of a rotor system formed of the rotor and the impeller is moved to the magnetic rotor side, that is, the rear end of the impeller, but the ceramic bearing is installed in the inner space of the axial hub part, that is, the length and the position of the ceramic bearing is not consistent with the centroid of the rotor system so that the weight of the rotor system may cause a big moment applying on ceramic bearing, and the lifecycle of the pump may not be ensured.
Case 6:
U.S. Pat. No. 7,101,158B2: Hydraulic balancing magnetically driven centrifugal pump, 2001. The invention describes a problem of an axial thrust balance of a magnetic drive pump. The figure in the invention distinctly shows that when the diameter of a stationary shaft is fixed and a triangle front support is assembled in the inner space of an inlet, the excess outer diameter of a front shaft seat of the triangle front support affects an inlet channel of an impeller and reduces the performance of the pump. Therefore, the inner diameter of an inlet channel of the pump must be increased to reduce the flow resistance of the inlet of the impeller.
Case 7:
U.S. Pat. No. 7,249,939B2: Rear casing arrangement for magnetic drive pump, 2007. The invention discloses a magnetic drive pump including a stationary shaft with a double-sided-support or a rotary shaft. The invention indicates that the strength of a containment shell of the magnetic drive pump is a problem which needs to be further concerned about. The gap of an out rotor and an inner rotor is narrow and limited, and plastic material with high corrosion resistance is usually thermoplastic, so the strength of the plastic material is reduced with increasing temperature. In prior art, a second reinforce layer is installed on the outer surface of the anti-corrosion layer of the containment shell. In this patent, a nonmetallic banding circular reinforce component is installed between two layer structures or on the outer surfaces of the two layer structures which are on a lateral cylindrical portion so that the strength of a lateral shell column part of the containment shell is enhanced. This method is better than the conventional method enabling a fiber stripe to wind up around the circumference into multiple layers. But this method may not effectively overcome the bending deformation of the shell column part due to a radial force applying to a rear shaft seat of the containment shell, and furthermore the invention also indirectly confirms that the supporting of the stationary shaft is affected by the strength of the shell column part of the containment shell.
Case 8:
U.S. Pat. No. 6,293,772B1: Containment member for a magnetic-drive centrifugal pump, 2001. The patent is applied to a metal magnetic drive pump including an anti-corrosion casing liner, and distinctly indicates that the strength of a plastic triangle front support of the magnetic drive pump and that of a containment shell of the magnetic drive pump both need to be further concerned. The triangle front support often affects an inlet channel of an impeller so that the performance of the pump is reduced. The strength of the containment shell not only resists fluid pressure but also offers the support for a stationary shaft. The invention is that a disc-shaped metal reinforce component is embedded between a inner layer and a outer layer structure at a bottom side of the containment shell, a radial force which applies to the cantilever stationary shaft may evenly transmit to a shell column part of the containment shell, and furthermore the reinforce component includes an extending portion having smaller diameter and extending inwardly in an axial direction for enhancing the support and the handling of the stationary shaft, so that the strength of the containment shell may support the stationary shaft in a cantilever way. Therefore, the cantilever stationary shaft without the triangle front support help meet lower NPSHr requirement, and has sufficient strength. However, the invention does not distinctly describe the strength of the lateral shell column part of the containment shell for preventing the stationary shaft from un-positioned after the reinforcement.
To sum up, as for the magnetic drive pump including the pump parts only made of fluoropolymer or the parts with fluoropolymer liner, the problem of the structure and the strength of the stationary shaft are shown as follows:
1. The weakness of the strength of the fluoropolymer material.
2. The stiffness requirement for the supporting structure of the stationary shaft.
3. The flow resistance problem of the inlet channel.
4. The problem of Net Positive Suction Head required (NPSHr) of the inlet channel of the impeller.
5. The strength problem of the containment shell including its shell column part and its bottom part.
However, each of the solutions in the above-mentioned patents may not meet the requirement that the stationary shaft with high stiffness may transfer the fluid at high temperature, 200° C. In order to solve the above-mentioned problem, a magnetic drive pump is disclosed in this invention. The following is the detailed description of the present invention: